The present invention relates to a process for preparing stereoisomerically enriched 3-heteroaryl-3-hydroxypropionic acid derivatives by reducing 3-heteroaryl-3-oxopropionic acid derivatives in the presence of ruthenium-containing catalysts.
Stereoisomerically enriched 3-hydroxypropionic acid derivatives, in particular those which bear a heteroaryl radical in the 3-position, are valuable intermediates, for example, in the preparation of liquid-crystalline compounds, agrochemicals and pharmaceuticals.
Process for preparation comprising the catalytic reduction of ketones to stereoisomerically enriched secondary alcohols is known in principle. Useful reducing agents are typically molecular hydrogen or, in the case of transfer hydrogenations, organic hydrogen donors, for example formic acid or isopropanol. An advantage of transfer hydrogenations is that the safety precautions which have to be taken when handling highly flammable molecular hydrogen under pressure can be dispensed with. It is also generally possible to work at ambient pressure. A review of transfer hydrogenations as a method for catalytic reduction of ketones is given, for example, by Zassinovich et al. in Chem. Rev. 1992, 92, 1051-1069 and Noyori et al. in Ace. Chem. Res. 1997, 30, 97-102 and Wills et al. in Tetrahedron, Asymmetry, 1999, 2045.
Noyori et al. (JACS 1996, 118, 2521-2522, Ace. Chem. Res. 1997, 30, 97-102) describe the use of ruthenium complexes as catalysts and triethylamine/formic acid for the enantioselective reduction of simple ketones.
However, there still existed the need to provide an efficient process which allows the preparation of stereoisomerically enriched 3-heteroaryl-3-hydroxypropionic acid derivatives from 3-heteroaryl-3-oxopropionic acid derivatives.